There are strong economic and environmental incentives for converting carbon dioxide, methane and other low molecular weight sources of carbon into more useful chemicals and fuels. The Fischer-Tropsch process has been used for nearly a century to produce hydrocarbon fuel (gasoline, diesel, etc.) from gasified coal or natural gas at high temperatures and pressures assisted by catalysts. In that process, methane and steam can be reformed to Syngas (CO and H2), which then can be further converted to fuel in the Fischer-Tropsch process. In another process, methane and carbon dioxide can also be reformed to form CO and H2 for further processing into fuel. These processes require high temperatures and pressures and have high catalyst, energy and capital costs.
In the last few decades, methods have been developed for reforming low molecular weight carbon compounds, such as methane, propane, methanol and ethanol into higher molecular weight carbon compounds without using high temperature and pressure. These processes are described in numerous patents and scientific publications. Among the most promising processes being developed are those that employ non-thermal plasma to create free radicals, ions and/or activated molecules, which react to form larger, more useful molecules. These are discussed in the references in the “Reference” section later.
As described in detail in International Application PCT/US2012/033238 and U.S. Ser. No. 61/474,547, centrifugal force is commonly used to mix, move and/or separate fluids in reactors for chemical processes. Intense mixing of liquids and gases can be achieved in a centrifugal reactor, and energy to promote the desired reaction can be provided from outside the reactor or generated within it. The energy may be thermal, sonic, electric, radiant, mechanical or nuclear.
There are numerous ways to employ electrical energy to form ions and free radicals to initiate reactions. Electrical energy may be generated in the reactor by various means. An example is found in U.S. Pat. No. 7,806,947, “Liquid Hydrocarbon Fuel from Methane Assisted by Spontaneously Generated Voltage”, Gunnerman, et al. (“Gunnerman”), wherein methane is bubbled up through a grid of catalytic metal wires immersed in a liquid petroleum fraction. The wires are insulated from a grounded frame. As the mixture of gas and liquid bubbles up through the catalyst grid, an electrical potential is generated between the catalyst wires and the frame. This electrical activity creates free radicals, which produce new molecules from the methane and liquid petroleum fraction and convert the methane to a liquid fuel. This method is in commercial use.
Instead of being generated within the apparatus as in “Gunnerman”, the electrical energy may be provided from outside the reactor to form a high-voltage-induced plasma in the reactor. Low temperature plasmas induced by high voltage fields through a dielectric material are able to create ions, free radicals and activated molecules at ambient conditions with relatively low power requirements. In the reference titled “Carbon Dioxide Reforming with Methane in Low Temperature Plasmas”, the authors discuss use of corona discharge and dielectric barrier discharge (DBD) plasmas to dissociate CH4 and CO2 and to reform the gasses to CO and H2. A DBD cell or reactor is one in which two electrodes are separated by a dielectric, and the material to be treated passes through a space between the dielectric and one of the electrodes. The paper also compares plasma methods with the traditional thermal processes that require temperatures around 800° C. The plasma induced reaction proceeds as follows:CH4+CO2→2CO+2H2 (Syngas)
Numerous patents have been issued for devices and processes that use plasmas and arcs to initiate reactions to convert low molecular weight hydrocarbons and oxygenates into more useful higher molecular weight materials. A good overview of the state of the art is provided in US 2011/0190565, “Plasma Reactor for Gas to Liquid Fuel conversion”, Novoselov et al. (the '565 patent), where the reactants are subjected to a pulsed high voltage discharge to convert low molecular weight hydrocarbons into a liquid fuel. The inventor calls the reactor a “non-thermal, repetitively-pulsed gliding discharge reactor”. In the '565 patent, U.S. Pat. No. 7,033,551, “Apparatus and Method for Direct Conversion of Gaseous Hydrocarbons to Liquids”, Kong et al. is cited as an example of using a DBD reactor, coupled to an electrochemical cell, to achieve a similar result. U.S. Pat. No. 6,375,832, “Fuel Synthesis”, Eliasson et al. is cited in the '565 patent as an example of using a DBD reactor, packed with a solid catalyst, to convert methane and carbon dioxide into liquid fuel. The '565 patent also states that limiting factors of DBD systems are: “the non-chain character of the conversion processes . . . and the high activation energy (>400 KJ/mol.) of the primary radical formation process.” Also, low current and power density reduce the capability of the DBD systems. The gliding arc [or non-thermal plasma] process activates the molecules to “vibrationally- and rotationally-excited levels, which requires less energy than forming radicals as in a DBD reactor, and is a chain reaction.” The net result is a much lower energy requirement when a gliding arc, or direct non-thermal arc, is employed, as in the Centrifugal Fluid Ring Plasma Reactor.
The non-thermal arc process can be demonstrated in the laboratory with a simple device fashioned from a glass test tube or centrifuge tube (about 4.5×⅝ in.), two short pieces of tungsten/thorium welding rod, necessary tubing and stoppers and a source of variable high voltage, high frequency electric power. Water is put in the bottom of the tube to a depth of about ¾ in., and about two inches of light fuel such as kerosene is added above it. The two welding rods are inserted as opposing electrodes from the top so that their bottom ends are about 2 in. above the bottom of the glass tube. The electrodes are spaced about ⅛ in. apart at the bottom and about 9/16 in. apart at the top. The upper ends are attached to opposite poles of the power supply. A mixture of carbon dioxide and methane or propane is introduced below the water level through a glass tube. The top of the tube is sealed by suitable means. Gaseous products are removed from the top of the tube. After purging the system to remove all oxygen, electric power (5 to 10 Kv at 15 to 20 KHz) is applied to the electrodes. Voltage is increased until an arc is formed, and then reduced so that no “hot” arc is observed but power measurements indicate that plasma is formed. Carbon monoxide will be found in the gaseous effluent and waxy or oily material will form in the glass tube, which will show qualitatively that carbon dioxide is being reduced and high molecular weight material is being formed under these conditions.
None of the prior art discussed above has disclosed a centrifugal reactor for fluid reactants wherein a liquid ring is used to repeatedly move the mixed reactants back and forth through the rotor to contact them with catalysts and subject them to non-thermal plasma. However, centrifugal fluid ring reactors are disclosed in International Application Number PCT/US2012/033238, filed 4 Apr. 2012, which is incorporated in its entirety in this application by reference. This application claims improvements on the apparatus of PCT/US2012/033238.